Heretofore, only limited cure stability of one part and two part sealants and coatings based on blocked isocyanates has been achieved at the expense of mechanical properties of the cured sealants or coating compositions.
U.S. Pat. No. 3,267,078 to Damusis relates to limited shelf stabilities of from about 20 to 25 days at room temperature of blocked isocyanate-terminated prepolymers utilizing ketimine curing agents.
U.S. Pat. No. 4,507,443 to Barron et al relates to a sealant or coating composition made from blocked isocyanate-terminated prepolymers, a polyimine, and an organosilane as an adhesion promoter. Drying agents are also included to improve shelf stability.
Heretofore urethane sealant or coating compositions, such as the above, undergo a significant loss of curability, i.e., poor cure stability as measured by decreased Shore A and mechanical properties, and/or a significant increase in viscosity, i.e., poor viscosity stability.